1. The Field of the Invention
The present invention relates to a syringe apparatus for dispensing compositions such as dental cements. More particularly, the present invention is directed to syringes which enable compositions to be delivered without requiring significant exertion and preferably in relatively small quantities.
2. The Relevant Technology
An example of a widely used conventional syringe is shown in FIGS. 1A-1D at 10. Syringe 10 is shown having a barrel 20 with a plunger 50 slidably engaged therein. In order to appreciate certain limitations of syringes such as syringe 10, it is necessary to understand the details of the elements of such a syringe. These elements are briefly described hereinbelow.
Barrel 20 has a top grasping end 21 opposite a bottom end 29 with a substantially cylindrical sidewall 22 extending therebetween. Sidewall 22 has an exterior surface 23 and an interior surface 24. Interior surface 24 defines a substantially cylindrical chamber 25 for holding a composition. Chambers such as chamber 25 of barrel 20 are typically configured to hold about 1.2 cc of liquid.
Barrel 20 has a grasping handle 26 which is an annular flange extending radially outward from sidewall 22 at top grasping end 21 of barrel 20. Grasping handle 26 is centrally located around opening 27 which has the same diameter as the interior surface 24 of chamber 25.
A radial extension 28 extends integrally from sidewall 22 at bottom end 29 inward to define an exit port 32. Radial extension 28 acts as a stop for plunger 50 as plunger 50 is depressed.
Exit port 32 is the opening into channel 33 which enables channel 33 to communicate with chamber 25. Note that channel 33 is the interior surface of tapered exit tube 30. Channel 33 extends through tapered exit tube 30 and terminates at outlet 34.
Surrounding exit tube 30 is an attachment sleeve 36. Attachment sleeve 36 has an interior surface 37 with engagement threads 38 positioned thereon. A nozzle or tip 40, shown in FIGS. 1C and 1D, may be selectively attached to barrel 20 by coupling with threads 38. A variety of tips are available which may be attached such that channel 33 of exit tube 30 is in fluid communication with the tip for guided delivery of the composition to a desired location.
Tip 40 is configured to selectively attach in fluid communication with exit tube 30. To accomplish this end, tip 40 has a threaded end 42 for engagement with threads 38 of attachment sleeve 36. Opposite threaded end 42 is a flexible and angled spout 44 for guiding delivery of the composition to a desired location. It is of course envisioned that different sizes and shapes of spouts 44 can be used depending on the type and intended use of the composition. Furthermore, in alternative embodiments, tip 40 may be permanently attached to bottom end 29 or means other than threads may be used to attach different sizes and/or shapes of tips.
Plunger 50 has a distal lead end 51 opposite from a proximal pushing end 53 with a stem 52 extending therebetween. Radially extending outward at pushing end 53 is an annular pushing handle 58 used in advancing plunger 50. Plunger 50 is sized to be slidably received within chamber 25 through opening 27 at top grasping end 21. Plunger 50 has a length that permits it to be advanced to bottom end 29 such that a small portion of plunger 50 remains extending beyond opening 27.
Positioned at lead end 51 of plunger 50 is a cylindrically shaped sealing gasket 60. More particularly, gasket 60 is coupled to stem 52 via a gasket holder as shown in FIG. 1B at 64. Gasket 60 is made of a soft, compressible, sealing material, such as rubber, which allows the exterior surface of gasket 60 to seal against interior surface 24 of chamber 25 as plunger 50 is advanced within chamber 25 or selectively slid down to bottom end 29. Gasket holder 64 has a post 66 with a head element 65 integrally extending at one end and a base 67 integrally extending from the other end. Head element 65 and post 66 are inserted into an opening 62 of gasket 60 which expands such that head element 65 can be inserted therein and then elastically return to its original size such that head element 65 is removably held in gasket 60. Base 67 is connected to stem 52 to hold gasket holder 64 in position.
As discussed above, a small portion of plunger 50 remains extending beyond opening 27, as shown in FIG. 1D, when plunger 50 has been fully depressed such that gasket 60 contacts radial extension 28. The length of the portion of plunger 50 extending beyond opening 27 of syringe 10 when plunger 50 is fully depressed is about 1 cm. This configuration is typical for a conventional 1.2 cc syringe. Note that the length of the barrel is about 5 cm while the length of the plunger which includes gasket 60 is about 6 cm such that the ratio of the length of the plunger to the length of the chamber is 1.2:1.
While syringes such as syringe 10 are ideal for many uses, these syringes also have certain limitations. For example, in some instances it can be difficult to apply an adequate amount or the appropriate amount of force required to push the composition from chamber 25 into channel 33 and ultimately out of tip 40 attached to barrel 20. FIG. 1C depicts a loaded syringe with only gasket 60 and a portion of stem 52 in chamber 25 of barrel 20. As shown in FIG. 1C, a user typically grasps syringe 10 such that barrel 20 is held by the user's middle and index fingers as well as the user's thumb. As the plunger is depressed further and further into chamber 25 until gasket 60 contacts radial extension 28 to stop the depression of plunger 50 as shown in FIG. 1D, the user may have to exert increasing effort to dispense the composition. Accordingly, it becomes difficult to dispense the composition at a uniform rate and in a controlled manner. When a composition is relatively viscous, the difficulty experienced in applying either an adequate amount or the appropriate amount of force may further increase.
When an inappropriate amount of force is applied to pushing handle 58, gasket 60 may press against sidewall 22 of chamber 25 in a manner such that plunger 50 is not smoothly pushed into chamber 25 in a controlled manner. Plunger 50 may stop and then suddenly move downward in what is known as a stuttering effect. This can potentially result in delivery of excessive amounts of a composition which the practioner is attempting to deliver in a discrete amount.
Syringes such as syringe 10 are used for delivering many different types of compositions. Such syringes may be sold with preloaded compositions ready for immediate use. However, when it is necessary to deliver a two part composition having an A component and a B component which are mixed just before use, other syringes are typically utilized.
Upon mixing a formulation packaged in two parts, including A and B components, the A and B components typically undergo a chemical reaction which causes the resultant composition to "set up" in some desired manner. Such two part compositions are widely used in the dental field. For example, glass ionomer cements and resinous luting cements are frequently used for applications such as securing dental crowns in place. Temporary cements are also provided as two separate components which are mixed shortly before delivery. Also, some dental impressions are made using compositions of A and B components.
In order to work properly, it is important that the A and B components of these multi-component compositions be mixed together rapidly and thoroughly and in the right proportions. Failure to rapidly mix the components can result in loss of valuable working time due to the quick setting nature of the compositions. Furthermore, failure to rapidly mix the components can result in a non-homogenous composition due to uneven setting of the composition. Poorly mixed compositions can have less than optimum characteristics. For example, if a poorly mixed composition is used as a cement, it is possible that portions of the cement will fail to reach the chemical strength required for a long-term bond.
Problems of obtaining rapid and uniform mixing are often complicated by differences in the A and B components. Sometimes it is necessary to mix two liquids, while other times it is necessary to mix a powder with a liquid. Sometimes there are equal amounts of the A and B components, but other times there is more of one component than another. Sometimes the two components have similar viscosities, while at other times the two components have widely differing viscosities.
A syringe system for mixing two part compositions or A/B compositions is disclosed in U.S. Pat. No. 5,328,462 which issued to Dan E. Fischer and is owned by Ultradent Products, Inc. U.S. Pat. No. 5,328,462 is hereby incorporated by reference. An example of a syringe as disclosed in U.S. Pat. No. 5,328,462 is depicted in FIG. 2 of the present document at 10'. Note that the only difference between syringe 10 and syringe 10' is that barrel 20' has a vent hole 15 for venting air when plunger 50 is inserted into syringe barrel 20' after mixing.
U.S. Pat. No. 5,328,462 also discloses that the most effective mixing is achieved by delivering the components in a side-by-side fashion instead of one on top of the other. Such side-by-side loading is achieved through the use of a two-syringe device as disclosed in U.S. Pat. No. 5,328,462 and also in U.S. Pat. No. 5,290,259, which is also incorporated by reference. U.S. Pat. No. 5,290,259 also issued to Dan E. Fischer and is owned by Ultradent Products Inc. An example of a two-syringe device as detailed in these patents is shown in FIG. 3 at 110 with two syringe barrels at 120a and 120b. The output ends of syringe barrels 120a and 120b are fitted with tips 140a and 140b. Tips 140a and 140b are adapted at one end to be secured to the syringe barrels. The other end of each tips is adapted to be secured to a tubing members. Tubing members 146a and 146b are configured for delivering the two components into a syringe barrel such as barrel 50'. A collar 148 holds tubing members 146a and 146b together.
Prior to use, the syringe barrels 120a and 120b are filled with A and B components, respectively, of a two-component composition. The two plungers 150a and 150b are then simultaneously depressed while slowly withdrawing tubing members 146a and 146b from within the chamber of the barrel. This results in placement of material from each of syringe barrels side-by-side within the chamber.
After the two components have been delivered into syringe barrel 50' through the use of two-syringe device 110, it is necessary to mix the two components together. U.S. Pat. No. 5,328,462, which is referenced above, discloses various mixer elements for mixing the two components, an example of which is depicted in FIG. 4 at 170 in this document. Mixer element 170 also referred to as a spatula or paddle is inserted into barrel 50' and rotated until the two components are thoroughly mixed together. Other mixer elements are also disclosed in U.S. Pat. No. 5,697,903 which issued to Dan E. Fischer and is owned by Ultradent Products, Inc. U.S. Pat. No. 5,697,903, is hereby incorporated by reference.
Note that as stated in U.S. Pat. No. 5,328,462 at column 3, line 55 to column 4, line 10, the location of the vent hole limits the volume of material which can be dispensed from syringe 10'. If the vent hole is too high then air may be trapped and if it is too low then the composition may leak out of the vent hole. So the composition cannot be delivered into the barrel above the vent hole. Note that the structure of the barrel above the vent hole is resultingly utilized only to guide the plunger and not to hold a composition.
U.S. Pat. No. 5,665,066, which issued to Dan E. Fischer and is owned by Ultradent Products, Inc. discloses a configuration for avoiding the use of a vent hole in the barrel. U.S. Pat. No. 5,665,066, which is hereby incorporated by reference, discloses the use of a cylindrically shaped sealing gasket such as that shown at 60 which has a vent hole. The vented sealing gasket, which is referred to in U.S. Pat. No. 5,665,066 as a piston, is shown in FIG. 5 at 60". The vent hole of sealing gasket 60" is identified at 62". As shown in FIG. 5, the vented sealing gasket is pushed down toward the composition 90 to enable air to be released by pushing on the top surface 61" of gasket 60" with the distal end 56" of taper tip 54" of plunger 50". Once the composition is contacted by the bottom surface 68" of vented sealing gasket 60", distal end 56" of taper tip 54" of plunger 50" is inserted into vent hole 62" and plunger 50" is depressed against composition 90 to express the composition out of the syringe. A disadvantage of this system is that it is difficult to depress the vented sealing gasket very far into the barrel with plunger 50" so it is necessary to fill the barrel with as much of the composition as possible. Naturally, as more composition is delivered into the barrel the potential increases for incorporating air which must subsequently be released.
One problem associated with the delivery of two-part compositions with a two-syringe device as shown in FIG. 3 at 110 into a barrel such as barrel 50, 50', and 50" is that air may be introduced into the barrel due to the inability or failure of the ends of tubing members 146a and 146b to reach the bottom end of the barrel. The length of the tubing members can be increased but this also increases the amount of pressure required to deliver the components.
Undesired air bubbles can be introduced into the composition at various stages. During the mixing process, the stirring action of the spatula or similar mixing instrument, can introduce and cause air bubbles to be entrapped or entrained within the mixed composition. Furthermore, as mentioned above, transferring the mixed composition to a syringe can also cause air to become entrained within the composition. Depending on the composition and its intended use, the presence of air bubbles can have a detrimental affect. For example, when cements are used in the dental field, such as in bonding dental crowns, air bubbles in the composition can result in uneven layering or placement of the cement. In turn, the crown may not be uniformly secured and thus have a weaker long term bond. The presence of air bubbles can also effect the setting rate of the composition. That is, the portion of the composition exposed to the air bubbles may begin setting quicker than the remaining portion of the composition. This uneven setting can also influence the resulting effectiveness of the composition.
Another solution to the problems resulting from the introduction of air is presented in U.S. Pat. No. 5,697,903 which is referenced above. U.S. Pat. No. 5,697,903 discloses a syringe such as the syringe shown at 10'" in FIG. 6. Syringe 10" has a barrel 50'" with an access port 17. FIGS. 6 depicts access port 17 being utilized in conjunction with two-syringe device 110 to deliver a two part composition into chamber 25'". More specifically, tubing members 146a and 146b of two-syringe device 110 are shown extending into chamber 25'" to deliver the two part composition.
Access port 17 of syringe 10'" allows tubing members 146a and 146b to be shorter than when tubing members 146a and 146b must reach through opening 27 of syringe 10, 10' or 10" toward the bottom end of the barrel. As a result, less effort is required to deliver the two components into the barrel. Additionally, the tubing members can reach the radial extension of syringe 10'" and then begin filling as opposed to merely extending into the barrel as with the other syringes. Once tubing members 146a and 146b have contacted the radial extension and the two components have begun flowing, the tubing members can be withdrawn as the two components are laid down side by side until reaching a demarcation line shown at 19.
The side-ported syringe structure and associated methodology disclosed in U.S. Pat. No. 5,697,903 enables a syringe such as syringe 10'" to be very useful for minimizing the introduction of air into the composition. However, such a side-ported syringe also requires that all of the structure of the barrel above access port 17, more particularly above demarcation line 19, is used to guide the plunger and not to hold a composition.
In conclusion, a syringe is needed which enables a user to deliver a composition in a highly controlled manner. What is also needed in the art is a syringe which minimizes the entrainment of air when filled, especially with two component compositions. Additionally, such a syringe is needed which also minimizes plastic usage through minimizing the portion of the syringe barrel which merely guides the plunger and does not hold a composition.